top(1): another pass of cleanup

• avoid the need to call a function to get size of known array. I'll

likely re-arrange some of the indirect in a later to avoid the magic
constants.

• use correct type
• add const
• replace caddr_t with void*. This corrects an alignment warning.
• remove duplicated include from immediately prior commit

Under base clang we're now down to:

• 3 warning in top.c, 1 warning in mahcine.c, 4 warning in display.c,
• 1 warning in utils.c

Tested with base clang, gcc7, gcc9, base gcc (mips)